This invention relates to cardiac electrodes and more particularly to a multiple electrode pad for placement in contact with a patient's skin for receiving and transmitting electrical signals and methods for using the same.
Body surface electrodes are normally employed for non-invasively coupling a patient's intrinsic cardiac electrical activity with various medical diagnostic and therapeutic equipment. Electrical signals generated by the human heart appear in a characteristic pattern throughout the body and on its surface. Such intrinsic cardiac electrical activity may be measured by placing electrodes on the skin of the individual and measuring the voltage between a particular electrode and a reference potential or between selected bipolar pairs of electrodes. Well known bipolar pairs are typically located on patient's right arm (RA), left arm (LA), right leg (RL) (commonly used as a reference), and left leg (LL). Monopolar electrodes referenced properly are referred to as V leads and are positioned anatomically on a patient's chest according to an established convention. In heart monitoring and diagnosis, the voltage differential appearing between two such electrodes or between one electrode and the average of a group of other electrodes represents a particular perspective of the heart's electrical activity and is generally referred to as the ECG. Particular combinations of electrodes are called leads. For example, the leads which may be employed in a twelve lead system are: ##EQU1##
In one application, electrical signals produced by the heart are transferred by electrodes to a monitoring apparatus known as an electrocardiograph for further processing. In using electrodes to monitor the heart's electrical activity, it is important that the electrodes be positioned at the conventional anatomical positions to insure the acquisition of signals which will have universal diagnostic meaning. If electrodes are not positioned properly or if they do not make good contact with the patient's skin, the recorded data may be invalid.
While prior art ECG monitoring and diagnostic devices are capable of detecting failed electrodes, their response is to disconnect the failed electrode and substitute another electrode which is valid. While this relieved the problem of invalid data, it resulted in a reduction in the total data which is available. For example, while U.S. Pat. No. 4,577,639 discloses a system wherein a plurality of electrodes are connected, ECG data from only a single electrode pair is utilized. Should one electrode of the utilized pair fail, an unused electrode is substituted. Thus, for example, if Lead II (LL - RA) is being utilized and the RA electrode fails, the device would substitute another electrode, such as LA, to provide Lead III (LL - LA). However, this system was not wholly satisfactory because it did not permit several leads to be monitored simultaneously. Another prior art monitor is disclosed in U.S. Pat. No. 5,022,404 to comprise a system wherein failed electrodes are also disconnected, but this, too, can limit the number of leads being monitored.
Surface chest electrodes can also be used both diagnostically and therapeutically to transmit externally-generated electrical signals transcutaneously to a patient's heart. For example, cardiac impedance measuring, cardiac mapping, pacing and defibrillation are all medical procedures that utilize electrodes in this manner. Impedance measuring is a diagnostic procedure which measures cardiac output and detects mechanical events during a heartbeat, conveying information as to how well a patient's heart is pumping blood. For this procedure, an electrical current is passed through a first set of electrodes on a patient's skin in proximity to the heart and the voltage drop is measured across a second set of intervening electrodes. One of the difficulties with using electrodes for impedance measuring is that in order to achieve meaningful results, proper electrode placement is critical. Such proper electrode placement is generally not known in advance and some degree of electrode modification and repositioning is often beneficial to the signal quality.
Many abnormal cardiac conditions escape detection with present ECG monitoring or diagnostic systems which employ up to twelve leads. Cardiac spacial mapping enhances the probability that such conditions will be detected and is a procedure in which a multiplicity of voltage readings are made simultaneously from a large number of different sites on the patient's chest.
Another procedure that utilizes electrodes to send electrical signals across the patient's skin is external heart pacing. During a pacing procedure, an electrical current is applied transcutaneously to initiate a rhythmic pumping operation in the heart. The present practice of heart pacing is to place two large electrodes on the patient's chest and transcutaneously apply an electrical current without any specific concentration on the most sensitive portions of the heart.
Defibrillation is a medical procedure in which a relatively large electrical current is applied to a patient's heart that has temporarily ceased to function due to a chaotic electrical condition. For this purpose, it is necessary to provide two large contact areas for electrical current to enter and exit the patient's body.
Multiple electrode pads have been disclosed for the purpose of facilitating the simultaneous placement of a plurality of electrodes upon a patient's skin. One example of a prior art electrode pad is disclosed in U.S. Pat. No. 4,583,549. This ECG electrode pad utilizes six electrodes which are positioned on a patient's chest to correspond with an anatomically correct placement for precordial ECG electrodes. Another example is disclosed in U.S. Pat. No. 4,233,987, to comprise a curved strip with a plurality of electrodes arranged in curvilinear relation to one another for monitoring a patient's heart. A further example is illustrated in U.S. Pat. No. 4,763,660, which discloses a plurality of electrodes affixed to an elongated body structure for receiving and transmitting electrical signals to and from a patient.
These and other prior art electrode pads are not wholly satisfactory because even though they can be positioned relatively rapidly, there is no assurance that they would be accurately positioned in the stress of an emergency. Furthermore, prior art electrode pads were normally dedicated to a specific medical, diagnostic or therapeutic procedure, such as ECG monitoring, impedance measuring, pacing or defibrillation.